Allogeneic hematopoietic stem cell transplantation (HSCT) is a common treatment for patients with blood-derived cancers, which causes both desirable (graft-versus-tumor) and undesirable (graft-versus-host disease) effects. We have identified a population of CD8+ T cells that can mediate the graft-versus-tumor effect without inducing the potentially devastating side effect of graft-versus-host disease during allogeneic HSCT. In an effort to devise new strategies for improving outcomes of patients undergoing allogeneic HSCT, this project seeks to identify the features of this T cell population that contribute to the separation of these two simultaneously occurring immune responses during allogeneic HSCT.